In semiconductor manufacturing processes, PN interfaces made of different materials can be used on different applications. For instance, gallium nitride (GaN) has been widely used on light emitting diodes (LEDs). However, it is difficult to increase the carrier concentration of P-type GaN, and hence higher conductivity cannot be obtained. As a result, contact resistance between the P-type GaN and conductive later is too high to generate undesirable element characteristic problem, such as low light emission efficiency and high forward voltage. To remedy the aforesaid problem, a general approach is to fabricate a matching layer on the P-type GaN to enhance conductivity with other materials. One conventional technique is to position nickel gold (Ni/Au) material between the P-type GaN and electrode to reduce the resistance of the P-type GaN. Indium tin oxide (ITO) also can be used between the P-type GaN and electrode to reduce the resistance. Indium tin oxide (ITO) has greater transparency and can be easily transmitted by the light from LEDs to achieve higher luminance. However, based on present market requirements, contact resistance of Ni/Au or ITO still is too high, and thus the material still leaves a lot to be desired in terms of matching the P-type GaN.
Moreover, in order to solve the reflection problem of the light generated by the LEDs and emitted to the semiconductor, the surface of the P-type GaN is coarsened during the semiconductor manufacturing process to reduce light reflection. Under such a condition of the semiconductor manufacturing process, the resistance is obviously increased no matter Ni/Au or ITO is used. This is because that the coarsened surface of the P-type GaN has poor contact with Ni/Au or ITO and insufficient consistency to result in higher resistance. Referring to FIGS. 1A and 1B, a coarsened surface 1 is not smooth and flat. Hence when a matching layer is desired to grow, it cannot be fully joined to the coarsened surface 1, and a plurality of holes 2 are generated. As shown in FIG. 1B with an enlarged view, gaps formed between the holes 2 are obviously observed. Due to smaller conductive contact area, transverse electrical conductivity is undesirable, and contact resistance also increases.